Ground trainer for training aircraft crew members



May 9, 1950 F. M. BURELBACH ET AL 2,506,949

GROUND TRAINER FOR TRAINING AIRCRAFT CREW MEMBERS Filed June 25, 1946 9 Sheets-Sheet l Fi fw EUEEEEAE; J Ji MACS May 9, 1950 F. M. BURELBACH ET AL 2,506,949

GROUND TRAINER FOR TRAINING AIRCRAFT CREW MEMBERS Filed June 25, 1946 9 Sheets-Sheet 2 ATTORNEY May 9, 1950 F. M. BURELBACH ET A1. 2,506,949

GROUND TRAINER FOR TRAINING AIRCRAFT CREW MEMBERS 9 Sheets-Sheet 3 Filed June 25, 1946 f`. M BURE'LBCH INVENTORS. .JJ By m, .um

lMay 9, 1950. F. M. BURELBACH ET Al. 2,506,949

4 GROUND TRAINER F'OR TRAINING AIRCRAFT CREW MEMBERS Filed June 25, 1946 A 9 Sheets-Sheet 4 42/ l TRUE 4/7 Amspsfo Moron REDUCTION GEAR 80X REDl/C T/ON GEAR 60X M EURE /A/L/ENTORS. J J LUKACS Q) 5V AT TORNEY May 9, 1950 F. M. BURx-:LBACH ET AL 2,506,949

GROUND TRAINER FOR TRAINING AIRCRAFT CREW MEMBERS Filed June 25, 1946 9 Sheets-Sheet 5 E 5/ 6MB ,un

PROP FinT/-lv sir/rch' coc/rP/T F. M BURELBACH 'J J LUKACS ATTORNEY /A/ VEA/Tons:

.May 9, 1950 F. M. BURELBACH ET An. 2,506,949

GROUND TRAINER FOR TRAINING AIRCRAFT CREW MEMBERS 9 Sheets-Sheet 6 F. M BURELBACH J J UKACS Cv m m W m 6 A.. 9 l 5. 2 e m NG J 3@ m .u .Q QP* F WQ@ m AT TOR/VE? 4May 9, 1950 F. M. BURELBACH ET AL 2,506,949

GROUND TRAINER FOR TRAINING AIRCRAFT CREW MEMBERS 9 sheets-sheet '7 Filed June 25, 1946 BVGM. M

ATTORNEY May 9, 1950 F. M. BURELBACH ET A1. 2,506,949

GROUND TRAINER FOR TRAINING AIRCRAFT CREW MEMBERS 9 Sheets-Sheet 8 M. BURELBACH J J LUKCS 0o /NVENTORSS .Q ...Sl

Filed June 25, 1946 A 7` TORNEY May 9, 1950 F. M. BURELBACH ETAL 2,506,949

GROUND TRAINER FOR TRAINING AIRCRAFT CREW MEMBERS Filed. June 25, 1946 9 Sheets-Sheet 9 4 COWL FLAPS MOTOR UNIT M0701? UNI T F. M. BURELBACH /A/VEA/Tops.. J J LUKACS ATTORNEY Patented May 9, 1950 UNITED STATES PATENT FFHCE GROUND TRAINER FOR TRAINING AIRCRAFT CREW NEIVIBERS Application .lune 25, 1946, Serial No. .G7-9,069

V19 -.Claims.

'This invention relates to an aircraft trainer in which the operation of controls, similar to those of .a standard aircraft, by the members of the .crew causes the operation of instruments in the trainer l:and at an instructors desk to simulate the instrument operations .of an actual aircraft in flight whereby an aircraft crew may tbe given ground training to enable the crew rnernbers to coordinate their efforts to insure efficient aircraft operation under actual flying conditions ina regular aircraft. The invention relates more particularly to the circuits yand apparatus of the trainer for simulating the control of the engines `of a yniultiengned airplane to the oircu s under the control of a propeller featheringewitch ing with the actual equipment of aircraft. Foll lowing such basic training it has :been -lhe practice to .form crews from .such basically .trained personnel and to give vsuch crews .coordinated vtraining in the flight of actual aircraft which Lthey will later be assigned l.to fly in combat duty.

The larger aircraft, particularly irnultiengined .bomhers, are costly to build, vto-flyand to rnaintain'and the use of such airplanes for extended training purposes with crews who-may have `had little or -no experience in 4their operation, intro- `duces a great hasard both to the equipment and `to Lthe .operating personnel during ithe training yperiod and obviously withdraws such. airplanes `.from .their :more rvaluable use in actual compat service.

-TSince the membersof the crew have all had basic training in flying and in the operation of :the equipment Lof airplanes, the actual flying .hours in the e'type of airplane which they will .ultimately be assignedto fly may be materially --reducedthrough'the use of a ground trainer designed lto simulate all of the flight and operational functions of thetypefof airplane to which they #will later 'be assigned. vAfter coordinated .training in' such a ground trainer, the crew train- :ing may be completed within a comparatively few :hours Y.of flying in :an actual airplane.

'Lln Athe vapplication of fR. C. Davia-il. J .iiFogary and .-R. '0. Rippere Serial No. :54.2598", 4filed 2J une 2530, @9414, .a ground trainer .has` been disclosed in which an airplane V,crew may be trained to perform all of the flight and operational functions which would be required to actually fly and opera-te an lairplane which the trainer is ,designed to simulate ,and in the application vof J. J. Lukacs and W. B. `Strickler Serial No. 542,8i6, filed June 30, 1944, and in the application of C. E. Germanton, .Serial No. 622,070, led .October l2, 1945 ground trainers have been disclosed in which an airplane crew may be trained to perform all of the operational functions .which would be re- .vquired to control the engines and propellers .of a particular type of airplane.

lIt -is the object of the present invention to provide a trainer in which .the airplane crew may he trained zto perform all of the operational functions which would be required .to control the engines yand Y.propellers of a different type o f multeneined airplane.

In the trainer which has .been designed to attain the foregoing objects', circuits and apparatus have been provided which simulate the performance ofthe engines v,and propellers to develop Vthe same responses which would he obtained in the actual airplane lwhich the trainer simulates Or manifold .pressurc, R. P. M., brake horsepower, propeller pitch, propeller eiliciency, thrust, V fuel .,flOw, oil pressure, `fuel pressure, cylinder temperature and oil temperature. For training purposes the simulated warm up time for the .engines has been shortened. In controlling -the ,engine functions, the switches, circuit breakers .and fuel selector valves in the .trainer require the same 'manipulation and provide the .saine control Aof .simulated operation 4as in the airplane.

For a clearer understanding of the invention .reference may be had tothe following detailed description when read ,in kconnection with .the .accompanying drawings in which:

`lig. lshows inthe upper left portion thereof a schematic representation of the motor unit which provides the altitude simulation; in the :upper right portion the schematic representation .of the motor unit v,which provides the brake horsepower usimulation of one of the simulated engines and vparts ofthe brake horsepower .motor unitsof the other simulatedengines; in the .lower left portion the motor unit which simulates .the `control vof a'tachometer for one engine and in the Jlower right portion power supplies for the trainer.;

Fig. N2 shows in the upper right portion thereof the motor y unit which simulates the complete thrust of ail ofthe engines of the simulated Vairplane, inthe upper left portion thereof they motor 'unit which simulates the rate of fuel flow to one of the simulated engines and in the lower portion thereof the motor unit which simulates the manifold pressure response of one of the simulated engines;

Fig. 3 shows the upper portion thereof the motor unit and control circuit therefor which simulates the propeller pitch response of one of the simulated engines; in the lower left portion the propeller slip ratio motor unit for assisting in the determination of the propeller eiciency of the simulated engine driven propeller and in the lower right portion thereof the motor unit which simulates the functioning of the propeller governor appertaining to one of the engine driven propellers;

Fig. 4 shows in the upper portion thereof the motor unit which simulates the speed of operation of one of the simulated engines and in the lower portion thereof the motor unit which simulates the true airspeed of a simulated flight;

Fig. 5 shows to the left of the dot-dash line engine control circuit breakers and switches on the flight deck controllable by the pilot and to the right of the dot-dash line and in Fig. 6, circuits which simulate the starting and functioning of one of the engines in response to such controls;

Fig. 7 shows instruments, signal lamps and controls at an intructors desk;

Fig. 8 shows to the left of the dot-dash line instruments and controls at the pilots station on the flight deck; in the upper right portion the motor unit which simulates the production of oil pressure incident to the operation of one of the airplane engines and in the lower right portion the motor unit which simulates the production of fuel pressure in the fuel line of the carburetor of one of the airplane engines incident to the operation of a booster pump or the operation of the fuel pump driven by the engine;

Fig. 9 shows in the upper portion thereof the motor unit which simulates the production of cylinder and oil temperatures incident to the operation of an airplane engine and in the lower portion thereof the motor unit which simulates the operation. of the cowl naps of an airplane engine; and

Fig. 10 is a chart showing how the other figures of the drawing should be arranged to completely disclosethe invention.

The motor unit disclosed in Figs. 1 to 4, inclusive, are each of the type disclosed fully in Patent No. 2,428,767 granted to Albert, Davis, Gumley and Holden, on October 14, 1947. To simplify the drawing the control circuit of only one of the units, that is the propeller pitch motor unit of Fig. 3, has been disclosed'in detail, each of the other units being skeletonized to merely show the motor, reduction gear box, limit switches and such of the potentiometers and variable transformers or variacs driven by the motor as enter into the simulation of the operation of an engine. The motor unit disclosed in Fig. 3 comprises a first dual vacuum tube VTI which serves as a two stage resistance coupled amplifier to amplify the control signal applied to the control grid of the left unit from the slider of the gain control rheostat Rl which is connected to the input signal conductor 300, and to apply the amplified signal potential to the primary winding of the step-up input transformer T2. The amplied signal is impressed from the lower secondary winding of the transformer through the dual diode tube VTZ, serving as a full wave rectifier, upon the control grid of the thyratron tube MI and the signal is also impressed from the upper secondary winding of the transformer upon the control grid of the thyratron tube R. Grid biases are applied to the control grids of the thyratron tubes MI and R from the right secondary winding of the power supply transformer T3 through the dual diode tube VT3 and are adjusted by the grid bias adjusting rheostats R2 and R3.

Tube MI upon firing causes the transmission of positive impulses through the rotor circuit of the motor M from the volt phase p I bus bar I |590 I. Tube R upon firing causes the operation of the anode relay RV which in turn causes the operation of the stator reversing relay RVI. The stator winding of the motor is energized in a circuit over the contacts of relay RVI from the volt bus bar. Cathode heater current is supplied to the filaments of the tubes VTI, VT2, VT3 and R from the left secondary winding of the power supply transformer T3 and heating current is supplied to the filament of tube MI from the middle secondary winding of transformer T3. Anode potential is supplied to the anodes of tube VTI from the +130 volt bus bar, anode potential is supplied from the 60 cycle 115 volt source of phase pI potential from source IUD, over bus bar II5 pI through choke coil 36| to the anode of tube MI and through the ballast resistance lamp 302, through the winding of relay RV and choke coil 333 to the anode of tube R.

Grid biasing potentials are applied from the right secondary winding of transformer T3 through the diode rectifier tube VT3 and rheostats R2 and R3 to the control grids of tube MI and R.

The motor M through the reduction gear box 304 drives the shaft 305 in one or the other direction, dependent upon the operated or unop'- erated condition of relay RVI, at a slow speed, and through pairs of gears such as 306, 307 and 398, 309 drives the sliders of potentiometers PP'I and PP8. The shaft 305 also has secured thereto cams 3|!) and 3II which control the contact sets of the LI and L2 limit switches to cause the rotation of the motor M to cease when the sliders of the potentiometers approach their Nos. I and 3 winding terminals respectively. Certain of the motor units also are provided with other cam operated contact sets such as the contact set NUL operable by the cam SI2 secured to the slider shaft of the potentiometer PP'I.

The cylinder and oil temperature motor unit of Fig. 9 is similar to that just described except that the motor COTM thereof is of the shaded pole Yalternating current type, the stator winding of which is energized from the 115 volt supply circuit of the trainer and the shaded pole wind'- ings of which may be selectively short circuited to cause the motor to turn in one or the other direction dependent upon the operated or unoperated condition of the R2 relay 900 and the operated condition of the RI relay 90|. The motor CFM of the cowl flaps motor unit of Fig. 9 is also of the alternating current shaded pole type, the shaded pole windings of which are directly under the contcol of the O and C relays 902 and 933 controlled in turn from the Cowl flaps control switch 800 on the pilots pedestal.

The motors OPM and FPM of the engine oil pressure and fuel pressure motor units of Fig. 8 are of the reversible universal type, the stator windings of which are energized by potential of 60 volts supplied from the full secondary winding of the power transformer T8 and the rotor windings of which may be energized by potentials `of 'the same or Yreverse phase as supplied to the sta- .tor 'winding under the control of relays whereby the motors may be caused to rotate in one or the .other direction at diiierent speeds.

' The iuel flow, manifold pressure, fuel pressure, oil pressure and cowl aps indicators on the plots and instructors instrument panels are .driven by synchroreceivers connected over telemetric systems with synchrotransmitters associat- .ed With `the corresponding motor units, such telemetric systems being supplied with 40G cycle 'power from the ZiltC bus bar. The tachometers .on the pilots and instructors instrument panels are `driven in the same manner as they would be driven in an actual airplane from tachoineter generators associated with the tachometer motor unit. The cylinder temperature and oil temperature indicators are controlled by direct current potentiometers associated with the cylinder and oil temperature motor unit. it is to 'be under- .stood .that duplicates of these indicators and the motor units for controlling them would be pro vided vfor each .engine to be simulated.

The engine throttles have the same appearance in the trainer that they would have in an actual airplane but each throttle is modified to control ,thesliders of four potentiometers. The carburetor mixture controls have also been modified by the addi-tion .of cams to each such control ior :operating contact sets.

Preparing the-trainer ,for operation tion thereby causing the operation or the MB l Arelay dei! of Fig. 5. The fuel selector valves (not shown) must beset to select tank. of fuel ior .each engine as represented by the operation of the :F.S relay Elli of Fig. 8 for the No. i engine and VVa fuel booster pump must be started to cause `simulation of the application of fuel pressure at the-carburetor of engine represented by theoperation of the BP relays@ of Fig. S for the vNo. -I engine. Also the circuit breakerswitches quired for the operation ci the trainer should be closed. Some oi" these circuit breakers are represented at Eil! to inclusive, of V5, thereby :causing the operation of the associated circuit ,breaker relays 5G23 and inclusive. All controls at .the instructor-fs desk, Fig. 7, should also .bein their normal condition.

Before the engines are started and with a ground condition of iiight simulated hy the trainenthe manifold pressure indicators Sie and .,116 on .the pilots and instructors instrument panelsfshould show the atmospheric pressure at the ground level, assumed to be sea level. To acconfiplish this a phase signal potential is applied l.tothe signal input conductoril! of the manifold pressure motor unit of Fig. Since the manin .fold pressure at this time is solely a function oi altitude, the potential applied to conductor 2,53 vis derived at the slider of potentiometer Alli of .the ,altimeter motor unit of 1 which will at .this time be positioned at the No. I terminal of .the potentiometer winding. The potentiometer .Winding is energized in circuit 'from a tap be- .;tweenthe resistors ill and of the potential .divider extending from the 40o! bus bar through such resistors to ground, through the potentiom- ,eter winding andresistor its to ground. Poten- :tialderived at the slider ci this potentiometer is then applied in parallel through resistor' its to ground and overconductor i@ 5, ,over the inner upper back contact of the AS relay'lS which will 'be unoperated since there is no simulated airspeed, over the upper back contact of the ES'I'I relay lSH2 since the No. l engine is assumed to have not started, and through resistor 814 Ato the signal input conductor 25u of the manifold pressure motor unit.

In response to this signal the motor unit will operate until the potential oi phase p2 derived at the slider of the balancing potentiometer MP4 rand applied to conductor 25S through resistor 25| balances the signal potential or phase fpl. To derive this balancing potential, the winding of potentiometer MP4 is energized in a circuit from the Mp2 bus bar, through resistor 252, through the winding of the potentiometer over conductor 253, over the upper back contact of the vES'TZ relay till and through resistor SIG to ground. `Shaft o f the motor unit will thereby be rotated to a position representative of the manifold pres'- sure of 30 inches of mercury. To indicate this manifold pressure, the manifold pressure indicators 'H5 and 8l@ are operated by the associated synchroreceivers 'lll and 3H which are coupled over conductors of the cable ll 3 with the synchrotransmitter 255 driven through gears 256 and 251 from the shaft 254 of the manifold pressure motor unit.

Engine starting To prepare an engine for starting, the battery Vsvvitch should be closed as above stated to thereby vcause the operation of the MB relay 5M, the mixture control switch Eile should -be in its idle cut-off position, as disclosed, whereby a circuit is .established from ground over .the normal contacts associated with cam thence over conductor l B and through the winding of the ICO relay Elli! to `battery and the ignition switch 52e should be in its Both position in which the IGR and l.lGfL relays Gill and will be permitted to operate. Relay Gill is connected in a circuit from Vground through its winding and through resistor .04 to battery and relay 552 is connected in a circuit .from ground through its winding and resistor BH3 .to battery, but the windings of these relays are normally shunted to groundover conductors ifliiand E535 and overnormally closed contacts of ythe vignition switch 52h. When, however, the switchis moved to its Both position, ground is removedfrorn both conductors and 553B and .relays liti! and 582 operate. The operation oi the 'ICO relay llll, the IGR relay EN, the IGL relay 5&2 close circuits over conductors E01, 5&8 and El!!! through the ICO, Ignition right magneto and Ignition left magneto lamps at the instructors desk to battery whereby such lamps light to inform the instructor lthat the pilot has set the -miXture and ignition controls preparatory vto starting the engine. Relay upon operating establishes the operating circuit `for the ICOI relay 633 which may be traced from ground over the upper inner front contact oi relay ililfover the upper back contact of the RPM .relay E39 and thence through fthe windingof relay cl-to battery. Relay 633 upon operating locks over its lower contacts directly to ground over the upper inner front Contact of relay Sllt.

Before the priming oi the engine may be simulated, Afuel pressure must be established Yby the operation of a selector valve and ka booster resulting in the operation oi the FS and relays l and ol the fuel pressure motor kunit previously stated and as fully'disclosed and described in the application of C. D.

'Koechling Serial-No. '66E-,025, led -April 26,1946.

andere 2' This application has matured into Patent No. 2,491,668, dated December 20, 1949. With these relays operated a circuit is established for the ST relay 853 of the fuel pressure motor unit from ground over the lower contacts of the FS relay 80|, over the lower contacts of the BP relay 352 and through the winding of relay 853 to battery. Relay 853 thereupon operates and establishes a `circuit extending from ground over its upper front contact, over the back contact of the UL relay 854 and through the winding of the IFP relay 305 to battery. Relay 335 thereupon operates and establishes a circuit through the rotor of motor FPM which may be traced from the ,ground terminal of the secondary winding of :transformer T8, through such secondary wind- :ing to the 25-volt tap thereof, thence through the rotor winding of the motor and over the front xcontacts of relay 855 to ground and, since the .stator winding of the motor is bridged across the secondary winding of transformer T8, the motor vr-will now operate to turn the shaft 8&6 at a slow ;speed in a clockwise direction representative of ;an increase in the fuel pressure in the fuel line ito the carburetor of the engine, assumed to be :the No. i of the four engines. When the shaft has been rotated to a position representative of :a pressure of 17 pounds per square inch the cam 801 will operate the springs of the Contact set UL to their alternate position thereby establishing a circuit from ground over the inner upper front contact of relay 353, over such cam operated contacts and through the winding of the UL relay 834 to battery, whereupon such relay will operate and lock to ground over the inner upper front contact of relay 833 and at its upper back contact will open the previously traced circuit of relay 855. Relay 895 thereupon releases to open the rotor circuit of motor FPM and such motor thereupon comes to rest. The rotation of shaft 85S has also been instrumental through gears 833 and 833 in rotating the rotor of the synchrotransmitter Si@ thereby causing the synchroreceiver 3H to operate and to set the fuel pressure indicator 812 on the pilots instrument 'panel and the synchroreceiver 1 I I to operate and set the fuel pressure indicator 'H2 at the in- ;structors desk over conductors of cable 8l3 to :indicate a fuel pressure of 17 pounds per square zinch. As soon as shaft 355 moves from normal or 1.the position representative of zero pounds fuel pressure, cam 82I permits the closure of the conitact set associated therewith, thereby establishing an obvious circuit for the LL relay 322.

The fuel pressure motor units (not shown) associated with the Nos. 2, 3 and (i engines, function in a similar manner, thereby causing the fuel pressure indicators for such engines at the pilots and instructors instrument panels to indicate similar fuel pressures of 17 pounds per square inch in the fuel lines extending to the carburetors of the Nos. 2, 3 and 5 engines.

Upon observing that there is fuel pressure for priming each of the engines, the pilot will proceed to start each of the engines in the usual order of precedence. T start the No. I engine, the pilot operates the prime switch 52| thereby establishing the circuit of the PRM relay 522 in simulation of the operation of the solenoid operated Valve on the carburetor which admits raw fuel from the carburetor to the intake manifolds -of the top cylinders of the engine. With relay -822 operated, representative of the presence of fuel at the carburetor, the operation of relay 522 establishes a circuit from ground over its upper contacts and conductor 523 of cable 532 and through the Primer lamp at the instru'ctors desk to battery whereupon such lamp lights to inform' the instructor that the prime switch for tlie No. I engine has been closed. With the prime circuit breaker 531' closed as previously described, a, circuit is now established from ground over the Battery disable key at the instructors desk, over conductor 524 of cable 532, over contacts of the RB relay 553 which operated upon the closure of the battery circuit breaker 552, over contacts of the MB relay 500, over Contact of the ENP relay 508, which operated upon the closure of the prime circuit breaker 5BI, over the lower contacts of the PRM relay 522, over conductor 533, over the lower contacts of the operated LL relay 822, over conductor 531i and through the winding of the PRMI relay 535 to battery.

Relay 535 upon operating establishes a circuit from ground over its lower contacts and conductor EIB and through the winding of the PRB/12 relay SII to battery whereupon the latter relay operates. Over its upper contacts relay 535 also applies potential of phase qui from the potential divider connected between the 40 pl bus bar through resistors 535 and 531, over its upper contacts to the signal input conductor 205 of the fuel flow motor unit of Fig. 2. Under the control of such signal potential, such motor unit functions to rotate its shaft 25| into a position representative of a fuel flow at the rate of pounds of fuel per hour as will be represented by the fuel flow indicators Bill and 'H4 on the pilots and instructors instrument panels, which indicators are driven by the synchroreceivers SI5 and H5, respectively, operated over the conductors of cable 252 through the operation of the synchrotransmitter 263 driven by the gears 204 and 255 from shaft 2t! of the fuel flow motor unit. The shaft 25| of the fuel ow motor unit also turns the slider of potentiometer FF? until a potential derived therefrom of phase p2 and applied through resistor 255 to the signal input conductor 255, balances the signal potential of phase pi applied to conductor 233. For deriving the balancing potential of phase (p2, the winding of potentiometer FF? is energized from the 5fp2 bus bar in a circuit through resistor 201 and the winding of the potentiometer to ground.

The release of the prime switch 52|' now permits the PRM and PRMi relays 522 and 535 to release but the PRM2 relay 5I I remains operated because of its locking circuit extending over its inner lower contact and the inner lower back contact of the ESTI relay E12 to ground.

When the start switch 533 is now closed, an obvious circuit is established for the STO relay 535 which, upon operating, at its lower contacts establishes a circuit over conductor 525 of cable 532 and through the Starter on lamp at the instructors desk to battery to inform the instructor that the pilot has closed the start switch. With the start circuit breaker closed as previously described, the operation of relay 535 also establishes the circuit for the STO relay 553 which may be traced as previously described from ground over the contacts of the Battery disable key at the instructors desk, over contacts of the MIB relay 555, thence over contacts of the ENST relay 5IIl and the upper contacts of relay 539 through the winding of the STO! relay 555 to battery. Relay 555 upon operating removes at its middle upper back contact the short circuit of capacitor 54| which extends from ground therethrough, through resistor 542, over the middle upper back contact of relay 540 and to ground over the inner lower back contact of the PS relay E563 whereupon condenser 54! starts to charge in a circuit from ground therethrough, through resistors 55172, 544 and 546, over the lower front contact of relay dell and the normal contacts of the TM relay 555 to the +130-volt bus bar. In approximately ten seconds the voltage across the capacitor will reach the breakdown potential of the gas tube GT and the tube will fire to complete a circuit from the +130-volt bus bar through the lower winding of relay 545 and through the tube, whereupon r'ela'y 545 will operate and lock over its upper winding and upper contacts to ground at the upper front contact of relay E. After waitm ingl about ten seconds, following ine operation of the start switch 538, to simulate fie time required for the electrically driven inertia starter used in an actual airplane to attain its full speed, which time, is measured by the operation of the tube GT, the pilot operates the mesh switch which in an actual airplane will control meshing of the starter with the engine. Upon the operation of switch 541, an obvious circuit is established for the STM relay 51th which upon operating establishes a circuit from ground over its lower contacts and conductor 52d of cable 532 to light the Starter mesh lamp at the instructors desk to inform the instructor that the starter meshing has been simulated. If relay de has at this time operated, representative of the elapse of the interval which should be measured to permit the starter to gain speed before being meshed with the engine, a circuit is now established from ground as previously traced at the contacts of the MB relay iiiiil, over contacts of the ENST` circuit breaker relay 5 i il, over the upper contacts or" relay 548, over the inner lower contacts of relay eilt, over the lower contacts of relay i545, over the inner upper front contact of relay 54B, over conductor El?, over the lower back contact of the EST! relay Blz and through the winding of the STM i relay 6|8 to battery.

With relay Eid operated, potential of phase qni is applied to the signal input conductor dilo of the RPM motor unit of Fig. 4. This potential is derived from the potential divider comprising resistors 62| and connected seriaily between the Dol bus bar and ground over the lower contacts of relay dit, lzrorn the junction point loe-x tween resistors 62i and 522 potential is derived and applied over the inner lower contacts of relay GQS and through resistors and $24 to ground. From the junction point between the latter resistors potential is derived and` applied over the inner lower back contact of the EST relay G25, over conductor and through the winding of the potentiometer PP'i of the propeller pitch motor unit and through resistor tit to ground. From the slider of this potentiometer, which will be assumed to be at the No. i termi 'nal oi its winding or in the increased RPM position, potential is applied over conductor over the upper front contact of relays ti and over the inner upper front contact of the PRL/l2 relay ti l, over conductor over the inner upper back contact of the PULE relay 512%, over conductor 528, over the upper contacts of relay sie and thence over conductor i523 and through resistor fidi to the input` signal conductor of the RPM 'motor unit. This potential `will be small and will cause' the motor of such motor unit to rotate the 'shaft do? into "a position representative of the speed at which the engine would operate under the control of the inertia starter. The

aecomo 10 shaft 402 will rotate until potential of phase p2 derived at the slider of the balancing potentiometer RPM and applied through resistor 403 to signal. input conductor 400, balances the phase pi signal potential. To derive the balancing po` tential, the winding of potentiometer RPi is connected from ground in parallel with resistor leid and through the resistor 495 to the No2 bus bar.

when the shaft 402 moves from its normal poition the cam to permits the contacts of the limit switch to move to their alternate .posi-v thereby closing an obvious circuit for the lay del. With relay 401 operated a circuit is established from ground over its upper confracts, conductor dit, and through the winding ci the RPM relay 53o to battery. Relay 630 upon operating establishes a circuit for the EST relay which will operate to simulate the operation of the engine under its own power, if fuel presis present as will be simulated by the operation of the LL relay 822 of the fuel pressure motor unit and if the ignition circuit has been closed as will be simulated'by the operation of either the IGR or the IGL relays Gili and 662. This circuit may be traced from ground over the inner lower contacts of the latter relays, over conductor over contacts of the Engine disable key at the instructors desk, over conductor 632, over next-to-inner lower contacts of the LL relay over conductor 8I8, thence over the lower contacts of the PRMZ relay 6| l, through the lower contacts of the RPM relay 630 and through the winding of the EST relay 625 to battery. The circuit from ground extending over the lower contacts of relay 6H is also extended over the inner upper contacts of relay BIS to the sound eriects circuit (not shown) whereupon such latter circuit becomes effective to simulate the engine noise.

The EST relay 625 upon operating establishes an obvious circuit over its lower contacts for the EST! relay SI2 which operates and in turn establishes a circuit over its lower contacts for the ESTZ relay 6 l 5. Relay E I 2, upon operating, opens at its inner lower back contacts, the locking circuit for the PRM2 relay which thereupon releases and opens at its lower back contact the circuit of the STMI relay BIB which thereupon releases. Following the release of relay 6l8, the start circuit to the sound eiects circuit is maintained over the inner lower front contact of relay 6 l 2.

When the ONA relay Mil of the RPM motor unit operated, a circuit was also established thereby from ground over its inner upper contacts, over conductor 408, through the winding of the F relay Ill of the tachometer motor unit and through the stator winding of the motor |01 of such unit to the |i30volt direct current bus bar thereby euere gizing the stator winding of the motor and causing relay "mit to operate and establish a circuit through the secondary winding of transformer 68, through the diode rectifier tube |09, through resistor lill, through rheostat H l and over the contacts of relay |06. A positive direct current signal potential which varies in accordance with the signal potential applied to the primary winding of transformer |88 is now derived at the slider of rheostat Il l and applied to the control grid of tube H2, superposed on an alternating current biasing potential derived at such slider by the application of alternating current from the left secondary winding of the transformer H3, through rheostat II4, resistor II8, rheostat III and through condensers IIS and IIB.

The signal potential applied to the primary winding of transformer |88 is derived from the slider of the RPS potentiometer of the RPM motor unit and varies with the engine speed. It is applied from such slider over conductor .155 through the primary winding of the input transformer |88 oi the tachometer motor unit, thence over conductor 4I8 and through resistor @Il to ground. To enable the derivation of potential at such slider, the winding of potentiometer RPS is connected through resistor 4I2 across the sec ondary winding of the constant voltage trans former shunted by resistors 4II and IIIA. The primary winding of both the constant voltage and power supply transformers 4I3 and II3 are connected to the filament supply bus .bars FI and F2.

The anode of tube II2 is supplied with 115-volt phase pI potential from the source |88 and thus when the tube II2 fires in response to the input signal, the rotor circuit of motor |81 is established from the II5pI bus bar through the tube I I2 to the mid-tap of the middle secondary winding of transformer I I3, thence through resistor I I1, through the rotor circuit of the motor to the II5p2 bus bar. The motor is thereby caused to rotate at a speed dependent upon the input signal as determined by the position of the slider of the RPQ potentiometer, or the simulated engine speed. The motor operates the tachometer generator I I 8 which is electrically coupled over conductors of cable IIS with the tachometers 'IIB and BIS on the instructors and pilots instrument panels and ythese tachometers then indicate the assumed engine speed.

As a further result of the operation of the ON relay 401 of the RPM motor unit, a circuit is established from ground over its lower contacts,

over conductor 4I5 and through the winding of f the RPM relay 820 of the engine oil pressure motor unit and thence to battery. Relay 820 thereupon operates establishing a circuit from ground over its upper contacts, over the back contact of the L2 relay 823, over the upper back contact of the NP relay 824 and through the winding of the IOP relay 825 to battery. Relay 825 thereupon operates and establishes the rotor circuit of motor 0PM from ground over the front contacts of relay 825 through the rotor circuit to the -volt tap of the secondary winding of transformer T8 and thence through the two lower sections of the secondary winding to ground. Since the stator winding of the motoris bridged across the secondary winding of the transformer, the motor now turns the shaft 825 in a direction representative of an increase in oil pressure until cam 821 operates the contacts of the limit switch L2 to their alternate position thereby establishing a circuit from ground over the inner lower contacts of relay 820, over the contacts of switch L2 and through the winding of the L2 relay 823 to battery. Relay 823 then operates to open thepreviously traced circuit of relay 825 to stop the motor. Relay 823 locks over its upper front contact under the control of relay 820.

The shaft 826 through the gears 828 and 829 operates a synchrotransmitter 830 which is coupled over conductors of cable 83| with the synchroreceivers 832 and 132 to' operate the oil pressure indicators 833 and-133 on the pilots and instructors instrument panels to show readings of 100 pounds per square'inch` Having simulated the. starting ofthe No. 1 engine as will be indicated by the reading of the tachometer BIS and the simulated engine noise,

the pilot restores the start and mesh switches 538 and 55'! thereby releasing the STO and STM re. lays 538 and 548, relay 5158 upon releasing in turn releasing the STMI relay SIS. The release of they PRMZ relay SII, which resulted from the operation of the ESTI relay SI2 as previously described, would result in the release of the EST, ESTI and ESTZ relays 525, SI2 and 6I5 and the simulated stopping of the engine, if the pilot did not operate the fuel mixture control 5 I5 from the idle cut-oli to the automatic rich position before the RPM relay 535 releases, since if the ICO relay 588 does not release, no circuit for the EST relay 625 is established. When, therefore, the pilot operates switch 5I5 to cause cams SI5 and 5I'I to operate their associated contact sets to their altornate positions, the previously traced circuit for the ICO relay 658 is opened and relay 600 releases and a circuit is established from ground over the alternate contacts of the contact sets operated by cams EIE and 5I'I and over the normal contacts oi the contact set associated with cam SIS and through the winding of the automatic rich (AR) relay 55I! to battery.

Relay Sii@ upon releasing, relases relay @33 and opens the circuit of the ICO lamp at the instructors desk. Relay 558 upon operating closes a circuit from ground over its inner lower con. tacts and conductor 52? of cable 532 for the Rich lamp at the instructors desk which lights to in-. form the instructor that the pilot has operated the mixture control SI5 to its automatic rich position. With relay 533 now released the circuit of the EST relay 525 extends from ground over the inner lower contacts of relays 58| and 582, over conductor -BI, over the contacts of the Disable engine key at the instructors desk, over conductor 552, over contacts of the LL relay 822, over conductor SIS, over the back contacts of the ICO! relay 533 and the lower contacts of the RPM relay 558 and through the winding of relay 525 to battery. Relay 625 thus remains operated and in turn maintains the ESTI and ESTZ relays 552 and 5I5 both operated.

Manifold pressure indication As soon as the EST, ESTI and ESTZ relays 625, @I2 and 5I5 operate as previously described, the circuit previously traced over which phase pI potential was applied to the input signal conductor 25E of the manifold pressure motor unit becomes opened at the upper back contact of relay 32 and the circuit over which phase p2 potential was applied to the winding ofthe balancing potentiometer MP4 of the manifold pressure motor unit becomes opened at the upper back contact of relay 5I5. However, new cir,- cuits are now effective for supplying control potentials to conductor 255 under the control of the throttle rheostats and in accordance with the assumed altitude of the flight, the setting of the supercharger control and the engine speed.

A potential of phase pl is applied to signal input conductor under the control of altimeter potentiometer AI, RPM potentiometer RPS and throttle potentiometer TP2. To attain this, the winding of the altimeter potentiometer AI is energized in a circuit from the bus bar 4 pl through the potentiometer winding and resistor IEIB to ground and the phase pI potential derived from the slider of the potentiometer is applied over conductor I2! through the winding of the throttle potentiometer TPI and resistor 55I to ground. It will be noted that the portion of this potentiometer between the center tap and the No. 3 terminal is shunted by the resistoi` 552 so that as the slider moves from the No. l' terminal toward the No. 3 terminal the potential of phase p l derived at such slider will vary at one rate until the center tap position is reached and will then vary at a slower rate as the slider approaches the No. 3 terminal. The potential derived at the slider oi potentiometer TPI is then applied.l over the back contact of the PIL relay 553, over conductor fill, through resistor illil, over the inner upper back contact of the SHR relay il i through the winding of potentiometer RPS oi the RPM motor unit, the -first 50 per cent of the winding of which is shunted by resistor ein?, thence over the lower back contact of relay die' and through resistor 132i to ground. With a portion of the winding oi' potentiometer shunted as just described, the potential derived at the slider of such potentiometer will increase at one rate as the simulated engine speed increases from Zero to about 1600 revolutions per minute and willv then increase at a faster rate as the engine speed increase further. This potential which in-` creases as the throttle opens ant.v increases as the RPMv of the engine increases is then applied from the slider of potentiometer RP3 over conductor.A (422,.over the middle upper front contact ofthe-ESTI relay SEE, through resistor @im and thence tothe signal input conductor 25d of the manifoldpressure motor unit.

At the same time potential of phase pl derived at the slider oi' potentiometer Ai of the altimeter motor unit and applied to conductor |2Iv isapplied through resistor 555 to the slider of throttle potential TF2 andv also over conductor" 555'y throughthe winding oi potentiometer RPZ of they RPM motor unit, the upper half oi which Winding. is-shunted by resistor $23, thence overl conductor 24' to ground. The winding ofthrottle potentiometer TPE is shunted-by resistor1 557i4 and the No. 3 terminal is connected tol ground so that as the slider is moved-tovvardthe'1 No. 3 terminal as the throttle is opened the shuntV ofthe-winding ofthe potentiometer RP? aiiordedA by thethrottle.- potentiometer TP2 becomes -increasingly more eective with the'result thattheA energization or" the winding of potentiometer RPZ-Y decreases as the throttle opens; Phase plpotential derived'at thefslider of potentiometerV RP2. will decrease at one rate as the simulatedl RPM of the eng-ine increases toA about 1600 revolutions per minute and will thereafter decrease at a slower rate as the RPM further increases. Thisderivedpotential is appliedv'over conductor 1125;` over the inner upper front contactofy the ESTE relay S52, through'resistor- 636- andthence to the signal input conductor 259 of the manifold pressure' motor" unit and decreases as the ythrottle opensI and decreases as the RPM increases'.`

Thus two potentials or phase e I` are applied to signal input conductor'e under the control 'of the throttle potentiometers TP! and TPE" and under theY control or" thev RPMv potentiometers RP2-and RPS: The summation of `these lpoten-` tials with the throttle abou-tten percent open foridling the engine at about 625 revolutions per minute, will be lessfthan thepotential of phase p2 which Valso becomes applied to the'signal input conductor' 25o-f through resistor 25!v from the slider of the manifold pressure potentiometer` MP4 fas-previously' described. However, withv the" EST2 relay SI5 now energized, the'shuntfof'thethrottlep'otentiometer TF3' which formerly ex-A 14 isted over the upper' back contact of relay SI5 is' no longer effective and as a consequencev the potential applied to the winding of potentiometer MP4 and consequently the potential applied from the slider of such potentiometer to conductor 250 is dependent upon the throttle opening. The circuit ove'r which' the winding of potentiometer MPif is now energized may be traced from ground through resistor SI5, over conductor G34, through the winding and over the slider of potentiometer TPE, over conductor 253 through the winding of potentiometer MP4, and through resistor "252 to the lilip bus bar. winding of potentiometer TPS is short circuited and thus until the throttle is 82 per cent closed this potentiometer has no effect on the energiza'tion of the MP4 potentiometer. After the throttle has opened to the 82 per cent position this phase (p2 potential will thus rst decrease and thereafter decrease and then increase as the manifold pressure increases.

Since the summation of the phase (pl potential applied to signal input conductor 250 at they tenA per cent throttle opening is less than the phase p2 potential now applied to such conductor the motor of the manifold pressure'motor unit will be operated in'a direction'representative of a reduction of manifold pressure to return the slider of potentiometer MP4 towardI the No. l terminal of its winding until the' potential of phase e2 applied from its slider again balances the summation of the phase pI signal potential. lhesliders'of the MPI, MP2 and MP3 potentiometers will be similarly adjusted and the synchr transmitter 255 will control the synchro-receivers 'Il'land SIT to reset-themanifold pressure in dicators 1 l 6 and 8I6 at the instructors and pilots instrumentpanels until they read about 2O Vinches of mercury;

The pilot now advances the throttle until the tachometer 819 shows an assumed engine speed of 1000 revolutions per minute. The opening of the throttle" causes the movement of the slider ofpotentiometer'TPllto cause 'an increase in the phase4 @l potential appliedthereover to signal input conductor 250'v of the manifold pressure; motor unit. To derive this potential which will vary-with the throttle opening, with themanifold pressure'and with the propeller pitch, potential of phase 'e I-is supplied from the Ilqil bus bar overthe lower contacts of the ESTZ relay`6l5, over conductory 531, through resistor 258,-thence by' oneV parallel path through the winding of potentiometer MPI of the manifold pressure motor unit to conductorV 2I5IV and thence through resistor 426 and through the true airspeed po tentiometerl TAS! I to ground. Also in parallel from resistor 258, through resistor 259, over conductor 250, through the'throttlev potentiometer TPfl, over conductor 42'! and through resistors 5128', vll'and 426-to ground at the potentiometer TASII. Until the slider of potentiometer MPI reaches the No. v3 terminal of its winding, a portion of its windingis shunted over its slider and throughresistor 259; The potential thus present at the slider of the throttle potentiometer TP4 will be determined bythe manifold pressure, by the throttle opening* and by the true airspeed of the simulatedfflight'. This potential is then applied `from conductor 260 over the inner lower contacts oi the EST relay- 625, over conductor E26," through the winding ofthe propeller pitch potentiometerPP'I and resistor 3l3 to ground whereby such potential isfurther modified in accordance withfthe simulated propellerpitch" The rst 82 per cent of the;

and applied over conductor 3| 4 and through' reY sistors 538 and 939 to ground, and in parallel with such resistors over the upper front contacts of relays 60| and 602, over the upper back contact of the ICO relay 690, the upper back contact of the PRM2 relay 6I I, conductor 521, over the inner upper back contacts of the PULI relay 549, conductor 928, over the middle lower front contact of the EST relay B25, conductor 529 and through resistor 40| to the signal input conductor 499 of the RPM motor unit.

In response to this signal the RPM motor unit operates until this phase pI signal potential becomes balanced by the phase p2 potential applied to conductor 490 from the slider of the balancing potentiometer RP|0 and thereby rotates the shaft 402 into a position representative of an engine speed of 1000 revolutions per minute.

With the opening of the throttle and the in- -v crease of the engine speed to 1000 revolutions per minute the potential of phase (pI applied from the slider of the potentiometer RPS to the signal input conductor 250 of the manifold pressure motor unit will increase and the potential of phase pI applied from the slider of potentiometer BP2 to conductor 250 will decrease and the summation of such potentials will be less than the phase pI summation potential applied to conductor 250 before the engine speed was increased to 1000 revolutions per minute and as a consequence the manifold pressure motor unit will cause its shaft 254 to rotate in a direction representative of a slight decrease in pressure below 20 inches of mercury as will be shown by g the manifold pressure indicators 'IIS and BIS.

' Simulation of cylinder and oz'l temperatures The temperature of the engine oil and engine cylinders is dependent upon the brake horsepower delivered by the motor, upon the fuel mixture and upon the open or closed condition of the engine cowl aps. It will be assumed that the cylinder temperature indicators '|34 and 834 at the instructors desk and on the pilots instrument panel, and the oil temperature indicators '|35 and 835 at the instructors desk and on the pilots instrument panel under normal conditions and before the engine is started all indicate a temperature of 15 degrees centigrade. It will also be assumed that the pilot has operated the cowl flaps switch 899 to its open position and has closed the cowl aps circuit breaker switch 836 thereby causing the operation of the circuit breaker (CF) relay 937. thereupon established from ground over the contacts of relay 83T, over the contacts of switch 800 in its open position, over conductor 838 and through the O relay 902 of the cowl flaps motor unit to battery. Relay 902 thereupon operates and short-circuits the right shaded pole winding 994 of the motor CFM and with the stator winding of such motor energized from the 115- volt supply 905, the motor turns the shaft 996 at a slow speed in such a direction as to move the sliders of the potentiometers CE2 and CFS toward the No. 3 terminals of their windings until if the control switch 800 is maintained closed for a suiicient time, the cam 901 will open the contacts of limit switch OP to release relay 902 and to stop the motor.

The rotation of shaft 906 through the gears 998 and 999 operates the telemetric transmitter CFT which over conductors of cable 9|0 controls the telemetric receivers |39 and 839 to op- A circuit is i6 crate the cowl flaps position indicators '|40 and 840 at the instructors desk and on the pilots instrument panel to indicate that the cowl iiaps have been opened.

The winding of the cowl flaps potentiometer CF2 is energized in a circuit from the 4|l p| bus bar over the inner lower contacts of the EST relay 845 of the engine oil pressure motor unit, over conductor 842, through resistor 9| i, through the winding oi potentiometer CF2 and through resistor 9 I 2 to ground so that upon the movement of the slider of such potentiometer, potential kof phase @I is applied therefrom through resistor 9I3 to the signal input conductor 9 I4 of the cylinder and oil temperature motor unit. The EST relay 84| is at this time operated over a circuit established from ground over the upper contacts of the ESTZ relay 555 and over conductor 640.

It is to be noted that this signal potential is not applied to the signal input conductor 9I4 until the engine starts and that the potential over conductor 9|4 is increased by the movement of the slider of the variac BH3 of the brake horsepower motor unit. To supply this augmented potential the winding of the variac is connected from ground to the wel bus bar by the operation of the BHP-ON relay |22 which operates as soon as the simulated engine starts to develop power as represented by the rotation of shaft |23 and the closure of the circuit of relay |22 by the operation of the contacts of limit switch LI to its alternate position through the movement of cam |24 as will later be described. The potential derived at the slider of variac BH3 is applied over conductor l |25, through resistors 558, 559, 590 and 56| to ground and a potential derived from such potential divider is applied from the junction point between resistors 559 and 560, over the lower front contacts of the AR relay 550, over the lower back contact of the AL relay 502 and through resistor 563 to the signal input conductor 9|4. This potential is not only increased to represent the increase in cylinder and oil temperature as the power output of the engine is increased, but is also increased when the AR relay 559 operates representative of the change of the :fuel mixture from idle cut-oir to automatic rich.

The instructor may also by the movement of the slider of rheostat 12| apply no potential or a predominant potential of either phase pI or phase p2 over conductor 'E22 of cable '|29 and through resistor 9 5 to the signal input conductor Sl of the cylinder and oil temperature motor unit to cause no change in the indicated cylinder and oil temperature indications or to cause an increase or decrease in the indicated temperature. For this purpose the No. I terminal of rheostat 72| is connected through resistor 139, over conductor 'E23 of cable 729 and over the upper contacts or the EST relay 84| of the engine oil pressure motor unit to the 40ml bus bar and the No. 3 terminal of rheostat 12| is connected through resistor 13| and over conductor 225 of cable '|29l tothe 40qp2 bus bar.

With the cowl flaps open, tending to slow down the heating up of the engine, the slider of rheostat 12| is set to cause a normal temperature indica-- tion of 15 degrees centigrade and when the slider of variac BH3 moves to a position representative of the power output of the engine at the assumed engine speed or 1000 revolutions per minute, the summation of the phase pI and p2 potentials applied to control conductor 9M will be a phase rpI potential which will be applied across the` amplifier gain control rheostat SIG. The phase 17 pl potential derived at the slider of rheostat SIG is applied to the control grid of the left unit of the dual amplier tube Sill, is amplified by thc cascaded units of the tube and is applied to the input transformer 918. Through the response of the tubes elli, 920 and 921 of the motor control circuit in a manner fully described in connection with propeller pitch motor unit of Fig. 3, the RI relay Sti is caused to operate and with tube 922 not firing in response to a phase (pl signal and consequently the R2 relay 90e not operated, the left shaded pole winding 923 of the motor COTM is short-circuited by a circuit extending over the upper contacts of relay 904, over the upper back contact of relay 900 and through the normal contacts of the L2 limit switch and the motor are now rotated toward the No. 3 terminals oi 'Y their windings. As the slider of balancing potentiometer BAL advances, potential of phase @E in increasing value is applied through resistor 25 to the signal input conductor Sie until when such potential balances the signal potential of phase pl applied to such conductor, no potential appears on the control grid of the left unit of amplifier tube dll and relay 90| thereupon releases and the motor COTM cornes to rest. For

deriving the potential of phase :p2 at the slider of potentiometer BAL, the potentiometer winding is energized over a circuit extending from the steil bus bar through resistor S and through the potentiometer winding to ground.

In response to the adjustment of the slider of potentiometer CYL-T, a circuit is established from battery through resistor 92'l, through t-.e potentiometer winding, through the Calibrating rheostat Q28, over conductor E25 of cable T23, through the cylinder temperature indicator '34 at the instructors desk and in parallel therewith over the conductors of cable itt, through the winding or indicator 834 at the pilots station and through resistor 943 to ground. Also in response to the adjustment of the slider of potentiometer OIL-Ti, a circuit is established from battery through the oil temperature indicator B on the pilots instrument panel, over conductor Seri, through resistor 933 and Calibrating rheostat 934,

through potentiometer OIL-Tl, over conductor' '26 of cable 'i129 and through rheostat l3l at the instructors desk to ground. Also in response to the adjustment of potentiometer OIL-T2 a circuit is established from battery through the oil ternperature indicator l35 at the instructors desk, over conductor l2l of cable 129, through resistor S29 and calibrating rheostat 30, through the potentiometer OIL-T2 and over conductor 'F28 of cable 129 to ground through the rheostat lSB at the instructors desk. Under the conditions assumed the cylinder temperature indicators 'its and B30 will slowly increase their readings from 15 degrees centigrade to about 100 degrees centigrade after an interval of about three minutes and the oil temperature indicators 135 and @35 will slowly increase their readings from 15 degrees centigrade to about Ll0 degrees centigrade after an elapse of about three minutes.

Decrease of oil pressure as the oil temperature increases As the shaft 924 rotates to a position representing an increase of oil temperature above 37 degrees centigrade cam 93| releases the PC 18 switch whereby a circuit is established from ground over such switch, over conductor 932 and through the winding of the T relay 845 of the engine oil pressure motor unit to battery. Relay 345 thereupon operates and, with L2 relay li operated as previously described, establishes a circuit from ground over its lower contacts over the lower back contact of the NP relay 32d, over the lower contacts of relay 823 f: and through the winding of the DOPI relay 845 to battery. Relay tilt now operates and closes a circuit extending over its contacts, over the back contacts of the IOPl, DOP and IOP relays del, Set and through the rotor winding of f, motor OPM and thence through the middle secondary winding of transformer T8 whereby the motor OPM is caused to rotate the shaft 825 at a slow speed and in a direction representative of a decrease in oil pressure until the cam 49 closes the NP contacts. When the NP contacts are closed a circuit is established from ground over the inner lower contacts of relay 820, over the upper front contacts of relay 823, over the upper contacts of relay S05, over the contacts of contact set NP and to battery through the winding of the NP relay E20. Relay 82 thereupon operates locking over its front contacts to ground over the inner lower contacts of relay 820, and opening at its lower back Contact the circuit of relay 806 which releases and stops the motor OPM. The synchro-transmitter 830 has now been readjusted through the rotation of shaft 82S to control the synchron'eceivers l32 and S32 to cause the oil pressure indicators 733 and 833 on the instructors and pilots instrument panels to show the reduction of oil pressure to about 85 pounds per square inch which would result in an actual engine due to the heating of the oil.

Magneto check-spark retarded Before simulating a take-off the two rnagnetos of each engine should be checked to determine if they are both operating. The pilot first applies the brakes of the trainer (not shown) and holds the stick (not shown) full back, and then advances the throttles of the engines until the tachometers, such as tachometer SIS, read 2300 revolutions per minute. 1n response to the advance of the throttle for the No. l engine the slider of the throttle potentiometer TP?, is advanced toward the No. 3 terminal of its winding thereby increasing the potential of phase el applied as previously described to control conductor fit@ of the RPM motor unit and such unit then functions as previously described to rotate the shaft t2 until the slider of the balancing potentiometer RPli has applied a balancing potential of phase oli to conductor lili? which balances the throttle potential of phase qui. At this time the shaft will have been set in a position representative of an engine speed of 2300 revolutions per minute and under the control or the potentiometer RPt the tachometer motor unit will be operated to cause the indicators H9 and SIS to read 2309 revolutions per minute.

As a result of the advance of the sliders of throttle potentiometers l and TPE and the new settings of the sliders of the RPM potentiometers BP2 and RPS for an engine speed of 2300 revolutions per minute the summation of the phase pi potentials applied to control cone ductor 250 of the manifold pressure motor unit first decreases at one rate until an engine speed of about 1100 revolutions per minute is reached aodeee 1 c 19 and then increases at an increased rate as de'- terrnined by the shunted center tapped poteritiorneters HP2 and RP' and the throttle poteritiometers TPI and TPZ. As a result of the decrease of potential applied to control conductor 2 50 until the engine speed eXceedsllO'O revolutions per minute, the manifold pressure motor unit V functions in the manner previously described to cause shaft 251i tov be rotated iii a direction representative of a decrease of inanifvold pressuretherebyvcausing the manifold pressure'indicators 'llt and 8l6 to decrease their 1 `eadin gsv to show a manifold pressure of about 20 inches of mercury. Thereafter as the throttle is opened and the engine speed increases to 2300 rvolutions per minute, and the summation potential increases, the manifold pressure` unit functions to cause the readings ofxtheindicators torincrea's'e to show a manifold Vpressure of about 277 inches of mercury. Thus lowering `and thenl increasing the manifold pressure as the throttle is opened, closely simulates the actual performance of an airplane engine.

increases to a value above 2200 revolutions perV minute cam 30 closes the contacts of the SR switch thereby establishing a circuit Afrom ground thereover, over conductor 4lil and through the winding of the SR relay lilllV to battery, Vwhereupon relay 64I operates. The. pilot will now turn the ignition switch 52@ to the L position in which ground will be connected to conductor BES and the IGR relay 36| willbe shunted down, simulating the disconnection of the right magneto, so that the engine will be fired by the left magneto only. `With the SR relay 64I now operated, the circuit from which a derived potential of phase (pi Was applied to signal input conductor 400 of the RPM motoruunit is: modified. The potential of phase pl derived at the slider of potentiometer PPI Vof the propeller pitch motor unit is now applied over conductor 3 I4, through resistor 638, over the upper front contact of the EST relay 625,V

Vpotential of phase pl thus applied to conductor 400 is thus slightly reduced in Value and the potential of phase p2 applied to conductor fte from the slider of balancing potentiometer RPI!) will be greater than the reduced potential of phase @l and the motor of the RPM motor unit will therefore be operated in such a direction as to return the slider of balancing potentiometer RP'IG toward the No. l terminal of its winding until the phase p2 potential becomes equal to the phase (pl signal potential. As a result of the operation of the motor driven shaft 4t2, the tachometer motor unit will be controlled by the potentiometer RPS to cause a resetting of the tachometers 135 and 855 to show a reduction in engine speed of 50 to 75 revolutions per minute. This simulates the reductionof engine speed resulting from the operation vof the engine on the left magneto only. While the IGR relay 50| lis shunted down the Ignition right magneto lamp at the instructors desk becomes extinguished to inform the instructor that the pilot has disabled the ignition circuit of the right magneto, Y

When the ignition switch 520 is returned to its Both position, relay y60| reoperates to reestablish the circuit previously traced over which potenen of phase el was yappiied to thesignai input conductor 'Seli of the RPM motor' unit whereupon such motor unit is controlled to again restore the readings of thetachometers to 2300 revolutions per minute. Relay Sill also causes *thel relighting of the Ignition right magneto lamp at the instructors desk. The pilot then turns the ignition switch 520 into the R position in which ground will be connected to conductor 606 and the IGL relay 602 will be shunted down, simulating the disconnection of the left magnetdso that the engine will be fired by theright magneto only. With the SR relay 64I now operated, the circuit from which a derived potential ofphase qui was applied to signal input conductor llt of the RPM motor unit is modied. Potential of phase pl derived. at the slider of potentiometer PP? lof the propeller pitch motor unit is now applied over conductor 3M, through resistor 638, over the upper front contact of the EST relay 325, over the front contact of the SR, relay Skil, over the back contact of the IGL relay S92 and thence as traced to signal input conductor tti) of the RPM motor unit. This motor unit now functions to rotate the shaft 402 into a position representative of a reduction of engine speed which is indicated by the resetting of the tachometers 'E35 and S35 to show a reduction of engine speed of 50 to 75 revolutions per minute. This simulates the reduction in engine speed resulting from the operation on the right magneto only. While the IGT., relay Gill is shunted down the Ignition left magneto lamp at the instructors' desk yis extinguished to inform the instructor that the pilot has disabled the ignition circuit of the left magneto. When the ignition switch 520 is restored to its Both position, relay Bill again reoperates causing the Ignition left magneto lamp to relight and to cause the indicated RPM to again increase to 2300 revolutions per minute.

Magneto check-spark advance When the pilot makes a magneto vcheck with the start advance condition simulated, the throttle is adjusted until an engine Yspeed of 2200 revolutions per minute is indicated. Under this condition the cam 630 on the shaft 4t2 of the RPM motor unit does not cause the closure of the previously traced circuitfof the SR relay ll. Consequently, when the ignition switch is moved to its L position and the IGR relay ll is released, the potential of phase pl derived at the slider ofthe potentiometer PPT of the propeller pitch motor unit will be applied through the potential divider comprising resistors 38 and 639 to ground and potential derived from such potential divider Will be applied from the upper terminal of resistor 538, over the upper back contact of relay till, over the upper back contact of relay etl, over the upperfront contact of rela-y 662, and thence as traced to the signal input conductor lill of the RPM motor unit. There will therefore be no reduction in the signal potential resulting from the release of the IGR relay Sl and therefore n'o reduction in the indicated engine speed from 2200 revolutions per minute. Similarly, when the ignition switch is moved to the R position and the IGL r'elay 502 is released, the potential of phase pl derived at the upper terminal of the` potential divider comprising resistors 638 and B39 will be applied over the upper back contact of relay 64I, over the upper back contact of relay 602 and thence as traced to signal input conductor 400 of the RPM motor unit. There will, therefore, be no' reduction in the signal potential resulting from the release of the IGL relay 602 and therefore no reduction in the indicated engine speed from 2200 revolutions per minute. The Ignition right magneto and Ignition left magneto lamps at the instructors desk will be extinguished as previously described upon the release of relays 60| and 602, respectively.

Engine simulation under 'talee-off conditions To simulate take-off the pilot releases the brakes, allows the control to return to its normal position, operates the super charger control 554 to its lower gear ratio position, checks to make sure that the propeller pitch control switch 554 is in its INC position and slowly advances the throttles toward their open position. When the control 55d is moved to its L position an obvious circuit is closed for the LR relay H which closes a circuit from ground over the contacts of the SC circuit breaker relay 512, over the contacts of relay 5l?, over conductor 518 and through the winding of the SI-IL relay 439 of the RPM motor unit to battery. Relay 439 operates and opens the locking circuit for the SHR relay 43B. Relay lill also lights a lamp (not shown) at the instructors desk indicative of the L position setting of control 554. It has been assumed that the propeller pitch of each propeller has been adjusted to its full increased RPM position but it was not explained how this was accomplished. It will be assumed that the propeller pitch has not previously been so adjusted and that to adjust it the pilot operates the switch 564 for each propeller to its INC position thereby establishing an obvious circuit for relay 565 which in turn establishes the circuit of the INC relay 56e, it being assumed that the circuit breaker relay Sill has been previously operated by the closure of the circuit breaker switch 501.

Relay 5% upon operating establishes a circuit from ground over its upper contacts, over conductor SI5 and the back contact of the H relay titl or" the propeller governor motor unit and through the right shaded pole winding of the motor GM of such unit to ground. With the stator winding of the motor GM energized from te Fi and F2 bus bars, the motor GM turns the shaft Sil at a slow speed, in a direction representative of an increase in propeller speed thereby moving the slider of the potentiometer PGM toward the No. 3 terminal of its winding. The winding of this propeller governor potentiometer being energized over a circuit from the flsqn bus bar, through resistor 3 I 8, through the winding of the potentiometer and resistor 3I9 to ground, the winding and resistor 3I9 being shunted by resistor 325, an increasing value of potential of phase o2 is derived from the slider of such potentiometer until when the slider approaches the No. s terminal the winding, cam 32| operates the contact set I-I to its alternate position thereby causing the operation of the H relay 315 and the consequent stopping of the motor GM.

With the INC relay 565 stili held operated by the continued operation of the switch 554 to its INC position and the H relay of the propeller governor motor unit operated, a circuit is now closed from ground over the lower contacts of relay over conductor 323, over the lower front contact of relay Sii?, over conductor 324 and through the Propeller limit lamp on the pilots pedestal to battery. A parallel circuit is also established from ground on conductor 323 over the inner lower front contact of relay 316, over conductor 525, and through the Propeller 22 limit lamp at the instructors desk to battery. When the Propeller limit lamps light, the pilot and instructor know that the propeller governor has caused the propeller pitch to be decreased to its full limit. The pilot will then return the switch 555 to its neutral position.

The phase c2 potential derived at the slider of potentiometer PG! i is applied over conductor 322, over the upper back contact of the PGP* relay 561, over the upper back contact of the FP relay 568, over conductor 5t?, over the inner upper back contact of the UF relay 5&3, over the inner upper back contact of the PTR relay Edil, through resistor 5455 to signal input conductor 350 of the propeller pitch motor unit. This unit is now controlled to rotate its shaft 355 in a direction representative of a reduction in pitch or an increase in RPM. When the shaft 3015 reaches a position representative of the reduction of propeller pitch to its lowest limit, cam @it operates the L! limit switch to the position disclosed to stop the motor M.

As a result of the advancement of the throttle the sliders of throttle potentiometers TPI and TPE move toward the No. 3 terminals of their windings with the result that the signal potential of phase ei applied to the signal input conductor of the manifold pressure motor unit under the control of the throttle potentiometer TPI increases and the phase el potential applied to conductor 25s under the control of potentiometer TP decreases until when the throttle becomes fully opened the latter potential becomes zero. The signal applied under the control of potentiometer TPI, however, supplies the main control of the indicated manifold pressure, the signal controlled by potentiometer TPZ providing the partly open throttle effect of manifold pressure indications increasing with a decrease in RPM.

.7 As the phase cpi potential applied to conductor increases the motor of the manifold pressure motor unit rota-tes shaft 254 and the slider of balancing potentiometer until the potential of phase p2 applied from the slider thereof to conductor 25s balances the signal potential of phase @l when the motor will stop. At this time the shaft will have rotated into a position representative of the manifold pressure of 54 inches of mercury which will be indicated by the manifold pressure indicators 'H5 and Bl.

As the manifold pressure increases and the slider of manifold pressure potentiometer MP! moves toward the No. 5 terminal of its winding, the phase ai potential applied over the circuit previously traced through resistor 2255 and through potentiometer MP1 to conductor '25s and thence to the signal input conductor 4GB of the RPM motor unit increases. This potential is further increased due to the increase in the resistance of the shunt of the potentiometer winding extending from conductor 265 through the throttle potentiometer TPfl, resistor 428, resistor and conductor El. Consequently the RPM motor unit will rotate its shaft 4t2 in a direction representative of an increase in RPM until the slider of balancing potentiometer RPil reaches a position in which potential of phase (p2 derived therefrom and applied to conductor dei! balances the signal potential of phase el when the motor of the RPM motor unit will stop. Under the control of potentiometer RP@ the tachometer motor unit will now have been controlled to cause the tachometers its and Gi? to show an engine speed of 2800 revolutions per minute.

As the RPM motor unit operates to represent 

